echo "Bash" > Scripting

What You will Learn

Basic Scripting
Variables
Default/InBuild Variables
Reading user input
Read/Write Files
Redirect Output
For Loop
If Statement
Functions
Curl
Tool to Debug Your Script

My FirST SCRIPT

Editors
- Use any text editor
- vi
- visual studio
- intellij etc
File Format should be .sh
File should have execution permission
First line:
- #!/bin/bash

Variable declarations

#A variable is a temporary store for a piece of information
#Unlike many other programming languages, Bash does not segregate its variables by "type."

FIRST_VARIABLE = "My first variable"
echo $FIRST_VARIABLE

MY_MESSAGE="Hello World"
MY_SHORT_MESSAGE=hi
MY_NUMBER=1
MY_PI=3.142
MY_OTHER_PI="3.142"
MY_MIXED=123abc

Command Line Arguments

$* All arguments on command line (" $1 $2 ...").

$0 First word; that is, command name
$1 First command line argument
$2 2nd command line argument
.
.
.
$n nth command line argument

$# Number of command-line arguments.

$@ All arguments

$$ Process number of current process. 

$? Exit code of prvious command

Reading user input

#!/bin/bash
# Ask the user for their name

echo Hello, who am I talking to?
read varname
echo It\'s nice to meet you $varname

##########################################################

#!/bin/bash
# Ask the user for login details

read -p 'Username: ' uservar
read -sp 'Password: ' passvar
echo
echo Thankyou $uservar we now have your login details

##########################################################

ExerCISE USER INPUT

Show message to user:
- "What cars do you like?"
- "Provide me 3 options:"
Read three input from user
Output of script:
- Your first car was: {First Input}
- Your second car was: {Second Input}
- Your third car was: {Third Input}

for loops

# looping through range

#!/bin/bash
for i in {1..10}
do
  echo "Looping ... number $i"
done

#########################################
# Exit when user say Bye

#!/bin/bash
INPUT_STRING=hello
while [ "$INPUT_STRING" != "bye" ]
do
  echo "Please type something in (bye to quit)"
  read INPUT_STRING
  echo "You typed: $INPUT_STRING"
done


##################################################
# Print all command line arguments

#!/bin/bash

for var in $@
do
    echo "$var"
done

if-then statements

#!/bin/bash

echo -n "Enter a number: "
read VAR

if [ $VAR -gt 10 ]
then
  echo "The variable is greater than 10."
elif [ $VAR -eq 10 ]
then
  echo "The variable is equal to 10."
else
  echo "The variable is less than 10."
fi


###################################

man test

Functions

#!/bin/bash
hello_world () {
   echo 'hello, world'
}

hello_world

##################################################
# Print max number

#!/bin/bash
function max ()
{
    if [ $1 -gt $2 ]
    then
        echo $1
    else
        echo $2
    fi
}

max 5 10

Practice: OUTput

#!/bin/bash

var1='A'
var2='B'

my_function () {
  local var1='C'
  var2=$1
  echo "Inside function: var1: $var1, var2: $var2"
}

echo "Before executing function: var1: $var1, var2: $var2"
my_function D
echo "After executing function: var1: $var1, var2: $var2"

REDIRECT OUTPUT

#Redirect to file
cat hello.txt > redirect.txt

#Append to file 
cat hello.txt >> redirect.txt

#Redirect one command output to another command input
cat hello.txt | grep text

#redirects stdout
echo test 1> afile.txt

#redirect stderr
test.sh 2> error.txt

READ File

#!/bin/bash
cat filename.txt | while read line
do
   echo $line
done

######################################################

#!/bin/bash
while read line
do
   echo $line
done < filename.txt

######################################################

#!/bin/bash
while IFS=' ' read -r line
do
   echo $line
done < filename.txt

curl

#curl is a command line tool to transfer data to or from a server. It support many protocols.

#Examples:
# HTTP GET
curl -X GET https://wwwegenciaeu.int-maui.sb.karmalab.net/checkout-service/base/version

#HTTP POST
curl -X POST \
  http://localhost:15672/api/exchanges/checkout/egencia.checkout.offline.operation5/publish \
  -H 'Authorization: Basic Z3Vlc3Q6Z3Vlc3Q=' \
  -H 'Content-Type: application/json' \
  -d '{
    "properties": {
        "content_encoding": "UTF-8",
        "content_type": "application/json"
    },
    "routing_key": "air",
    "payload_encoding": "string",
    "content_type": "application/json",
    "payload": "{\"record_locator\" : 50013401398,\"event_type\" : \"CANCEL\",\"product_id\" : 60000,\"event_source\" : \"SUPPLY\",\"product_type\": \"FLIGHT\" }"
}'

Debugging